29 finishes
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Transcript of 29 finishes
WOOD MATERIALS TECHNOLOGY
4th Edition
Chapter 29Finishes
Protects the wood from wear and tear
Prevents decay – fungus, insectsProvides a nice finished surfaceEnhances colourChanges the colour (staining)
Purpose of a finish
Surface preparation– Getting the surfaces smooth and
clean– Preparing the piece before
putting on the finish
Applying the finish– The steps in putting on the
different layers of chosen finish– Different finishes will have
slightly different steps
Surface preparation
Application of finish
Finishing stages
Rub out/remove pencil lines Scratches and marks can be removed
using a scraper Punch nails and pin below surface Fill nail holes and small cracks using a
suitable wood filler Sand the surfaces smooth using
sandpaper Sand end grain Start with 100 grit (medium)
sandpaper, then with 180 grit and finally 320 grit (very fine)
Always sand with the grain – avoid scratching the surface
Brush off all dust or use a tack cloth
Surface finish
Sandpaper (glass paper)
Composition of sandpaper– Grit is bonded to the
backing paper or card– The grit size is printed on
the back of the sandpaper
Types of abrasive
Always sand with the grain
Always sand end grain
Sanding
Advantages– Good inside and outside– Lots of colours available– Durable– Long-lasting– Easily-cleaned– Covers scratches and
defects well
Disadvantages– Hides the beauty of the
wood– Difficult to apply well– Needs good preparation– Can blister and peel
Paint
Prepare surfaces wellSeal knots with knottingApply primer to all surfacesFill cracks and holesApply 1 – 2 coats of
undercoat Sand lightlyApply final finish coatAllow each coat to dry fully
Painting wood
Why choose varnish?– Water-resistant – Scratch-resistant– Easily-cleaned – Clear finish enhances
the grain of the wood– Resists heat – Stains/coloured varnish
are available
Varnish
Apply the varnish with a brush/cloth, working with the grain
Cover all surfaces evenly, with no drips/runs
When the first coat is applied, allow to dry
Sand lightly between coats (denib) with very fine sandpaper or fine wire wool
Apply another coat of varnish evenly and leave to dry again
Repeat the process until you have three coats applied
Varnish – application
Microporous finishes
Breathable skinProtect the wood from the
weatherAllow moisture to evaporate
from the woodDo not flake or blisterEnvironmentally friendlyFor external use, e.g.
sheds/fences
Danish oil
Why choose Danish oil?– Easy to apply– Doesn't raise the grain– Gives a nice shine– Wood can be re-oiled– Suitable for outdoor use
Danish oil – application
Apply with a cloth, work oil well into the grain
Apply two or three coats and leave to dry overnight
De-nib any rough surfaces using light sandpaper
Apply another three coats of oilGradually build up the finish using
the above process
Wax finishes
Why choose wax?– Easy to apply– Does not raise the grain– Gives nice lustre/shine– Easy to renew– Allows polish to be built
up – No sanding between coats– Indoor use only
Wax finishes – application After surface finishing, seal the
wood with a wood sealer Using a clean dry cloth apply the
wax rubbing well into the wood Build up a number of coats before
letting the wax dry for a while Polish the surface to bring up a
shine Repeat the process to build up to a
high gloss shine Wax is a soft finish and is not water-
resistant, so it can only be used indoors
Lacquer
Applied by spraying Special equipment is
requiredProper extraction
system is requiredLacquer is harmful if
inhaled
Spray gun
Quiz
• Seals the wood • Prevents dirt getting in• Enhances the appearance
of the piece• Protects the wood from
wear and tear
Why is it necessary to apply a finish to a wooden artefact?
− White spirit
What is used to clean a brush after applying oil-based paint or varnish?
− Rub out/remove pencil lines− Scratches and marks can be removed using a scraper− Punch nails and pins − Fill nail holes and small cracks using a suitable wood filler− Sand the surfaces smooth using sandpaper− Sand end grain − Start with 100 grit (medium) sandpaper, then with 180 grit and finally 320 grit (very
fine)− Always sand with the grain – avoid scratching the surface− Brush off all dust or use a tack cloth
List the steps required to prepare a wooden item for an applied finish
• Microporous varnish, e.g. Fencelife− Protects the wood− Makes the wood look good− Allows the wood to breathe− Easy to apply− Prevents decay− Does not blister or flake
Suggest a finish suitable for a picnic table and give reasons for your choice
− Prepare the surface very well − Apply varnish to the surfaces with a brush
or cloth, work with the grain− Cover all surfaces evenly with no
drips/runs− When the first coat is applied, allow to dry− Sand lightly between coats with very fine
sandpaper or fine wire wool− Apply another coat of varnish evenly and
leave to dry again− Repeat the process until you have three
coats applied
Describe the steps in applying varnish to the unit shown